1. FIELD OF THE INVENTION
The present invention relates generally to devices for beam steering and scanning and, more particularly, to devices for beam steering and scanning which are electronic in character in that they incorporate no electromechanical or acousto-optical devices. The devices include an imaging cell which incorporates a solid-state cholesteric liquid crystal (CLC) element, a half-wave retarder and a source of circularly polarized light. The half-wave retarder is electronically controllable and converts electromagnetic energy (light) of one circular polarization to the other circular polarization when actuated and is disposed in the path of light emitted from the source. The CLC element is disposed at an angle (45.degree.) relative to the same light path and is designed to reflect light of one circular polarization and wavelength and transmit light of the other circular polarization at the same wavelength. When the source emits light of the other polarization and the half-wave retarder is unactuated, the CLC element transmits the resulting beam. When light of the other polarization is emitted and the half-wave retarder is actuated, the CLC element reflects the resulting beam of one polarization into a path which is orthogonal to the original path. By placing another of the above described imaging cells, for example, in the orthogonal path and incorporating a CLC element which is reflective of the other circular polarization at a 45.degree. angle in the orthogonal path, upon actuation of a half-wave retarder, the one polarization is converted to the other polarization and reflected into still another path by the CLC element.
By providing an array of the above described imaging cells and selectively accessing each of the rows of such an array with a column of similar cells and by selectively actuating the half-wave retarders associated with each column of the imaging cells, monochromatic or polychromatic light from single or multiple sources may be diverted to a selected cell and reflected from its CLC element or elements which are designed to reflect at a selected wavelength or wavelengths. In this way, electromagnetic energy may be steered or scanned without invoking any electromechanical or electroacoustic expedients. To the extent that scanning is achieved in a manner which eliminates large deflection angles, the long sought for fiat-panel display is achieved utilizing the devices of the present invention.
2. Description of the Prior Art
Generally, there are two well-known techniques for the steering and scanning of light beams. One is electromechanical and the other is acousto-optical. Both techniques have severe limitations. One such limitation is that arrangements incorporating these techniques require a large volume due to the small angle through which the light beam can be deflected. Thus, if it is desired to scan a length B, the deflection arrangement has to be positioned a distance, A, providing an A/B ratio larger than 1.
All known systems require an A/B ratio larger than 1 and to the extent that the arrangement of the present application can provide A/B ratios which are very much less than 1, the resulting structure may also be characterized as a flat-panel display. In the known scanning approaches, scanning speed is relatively sluggish due to the use of electromechanical or electro-acoustic elements. Because such devices are eliminated in the scanning arrangement of the present application, scanning speeds in the microsecond range are achievable.
U.S. Pat. 4,670,744 filed Mar. 14, 1985 and issued Jun. 2, 1987 in the name of T. Buzak incorporates variable optical retarders and liquid crystal chiral cells. This reference takes advantage of the reflective and transmissive characteristics of chiral cells as well as the ability of variable optical retarders to convert one circular polarization to the other circular polarization. However, when a beam containing image information is projected along a given path in which the chiral cells and retarders are disposed, the beam remains in that given path or is retroreflected along the same path. Opposed to this, the arrangements of the present application while they all incorporate the reflection-transmission characteristics of chiral cells, they all incorporate an ability to divert the reflected beams into other paths. To the extent that the Buzak reference seek to provide a three-dimensional display, all the images reflected must lie in a plane parallel to the planes of the chiral cells. Otherwise distortion and degradation of the reflected images would occur due to the required lateral displacement of the chiral cells. In other words, to provide the desired result, no diversion of the beam in the Buzak reference can be tolerated.
U.S. Pat. No. 5,221,982, filed Jul. 5, 1991 and issued on Jun. 22, 1993 to S. M. Faris is entitled Polarizing Wavelength Separator. The patent relates to a polarizing wavelength separating optical element in the form of a flat panel which causes each of a plurality of polychromatic optical beams from a source, entering at one surface and transmitted to another surface, to be converted, with high conversion efficiency, into circularly polarized, spectrally and spatially separated beams. The element is made of a periodic array of cells; each of the latter incorporating a plurality of subcells. One subcell functions as a broadband reflector, while each of the remaining subcells acts as a polarizing, wavelength selective reflector. Each subcell comprises a plurality of layers which are bonded together at their surfaces and are oriented at a 45.degree. angle relative to the horizontal surfaces of the panel. In each subcell, the plurality of layers comprise two cholesteric liquid crystal, CLC films, which reflect at a selected wavelength, at least one optical retarder and clear substrates which provide mechanical support. The thicknesses of the supporting substrates are designed to cause the beams transmitted through the element to be spatially separated by appropriate distances. In the reference, all the elements utilized in the panel are passive in character which constrain beams of electromagnetic energy into paths which are fixed for all time. In contradistinction to this, the present application, with it electronically controllable retarders, provides paths for electromagnetic energy which can be changed from instant-to-instant taking advantage of both the transmissive and reflective capabilities of CLC elements. The combination of a circularly polarized input with controllable retarders and associated CLC elements in the present invention provides the ability to scan a beam from point to point in a panel-like display or to steer a beam it can emanate from any location on an array of imaging cells. Strictly passive arrays with their fixed paths cannot achieve these results.